Various types of display pointers are known in the art. These include devices such as "light pens" or toy firing devices which can be pointed at or brought into propinquity with a given location on a display, such as a CRT display, for sensing illumination features thereof. Conventional light pens of this type require relatively complex synchronization circuitry for determining location on the display based on the time relationship of sensed illumination and of the time base of the display, including its synchronization pulses.
Prior art pointers of the type described hereinabove often require feedback in order to achieve location sensing. In practice a sensor on the pointer feeds back a signal that it sensed on the screen to a timing circuit in a computer. The timing circuit determines the time relationship of the sensed signal to the vertical and horizontal video synchronization signals of the screen and thus determines the position of the pointer on the screen.
The current state of the art is believed to be represented by the following U.S. Patents: U.S. Pat. Nos. 5,187,467; 5,184,115; 5,119,075; 4,608,601; 4,602,907; 4,190,851; 3,944,988; 3,832,693; 3,758,717; 3,659,281; 3,594,608; 3,576,574; 3,551,896; 3,543,240; 3,506,875; 3,505,561; 5,572,251; 5,138,304; 5,134,389; 5,051,736; 4,956,639; 4,922,236; 4,675,665; 4,591,841; 4,377,810 & 4,367,465.